U.S. Pat. No. 6,109,327 to the applicant of the present invention discloses a tire assembling-disassembling machine having a support base supporting a frusto-conical plate arranged to rotate, upon control, together with a control threaded shaft extending upwards from the support base where a pneumatic or electric motor suitable for driving the threaded shat is arranged. The wheel rim is inserted by the operator onto the control shaft and arranged to rest on the frusto-conical plate, the wheel rim being prevented from being removed from the shaft by a threaded bush or cone screwed onto the control shaft onto the wheel rim.
More particularly, a flanged support ring is keyed onto the control shaft and a counter-ring rests on it which is rigid in rotation with the frusto-conical plate. At the mutually facing surfaces of the flanged support ring and counter-ring mutually angularly spaced receiving seats are formed that extend tangentially. The receiving seats are delimited by four inclined-plane walls, i.e. two lower walls in the flanged support ring and two upper walls in the counter-ring. Preferably, a rolling element, e.g. a sphere or a roller, can be located in each receiving seat.
The counter-ring is mounted in such a way as to be able to effect limited controlled raising-lowering movements, and thus a friction engagement is established between ring and counter-ring. When the control shaft, and thus the flanged support ring, is set in rotation in one direction or in the other, the friction engagement due to the spheres located between ring and counter-ring is responsible for dragging in rotation also the counter-ring until the driving torque reaches a predetermined threshold value. At that point, each sphere will roll along the inclined walls in its respective receiving seat, which results in the counter ring and the wheel rim being raised with respect to the flanged ring. Thus, the wheel rim, becomes rigid in rotation with the frusto-conical plate. Such a structure ensures an efficient and stable rotation of the wheel rim on the plate even if the upper cone is not tightened against the wheel rim.
A device as that described above although, from one side, it provides a stable coupling between wheel rim and rotating plate without requiring special effort by the operator, from the other side it has a quite complex structure that, among other things, is difficult to assemble which means that highly trained operators must be employed.